An in vitro bioassay developed in this laboratory will be applied to study colony-formation by human tumor stem cells from primary explants. During the initial 2 years of research, the assay has proven capable of supporting colony growth from a wide variety of human cancers, and has proven amenable to drug sensitivity assays. The colony forming assay will be used to study the biological, kinetic, and cytogenetic properties of tumor stem cells, as well as their response to a variety of pharmacologic agents. Tumor cells from cancer patients' bone marrow aspirates, malignant effusions, and surgical samples of primaries and metastases will be studied from a variety of types of cancer. The fractional survival in vitro of human tumor stem cells to selected anticancer drugs will be studied in specific types of cancer with the aim of developing a predictive approach to cancer chemotherapy and new drug development. Clonal heterogeneity will be studied with cytogenetics as well as other approaches to gain further insights on mechanisms of resistance to chemotherapy.